Wood preservatives



Patented Oct. 8, 1946 Bror Olof Hager, Stockholm, Sweden,

assignor to Boliclens Gruvaktiebolag, Stockholm, Sweden, a. joint-stock company limited of Sweden No Drawing.

Application February 3, 1943, Se.-

rial No. 474,627. In Sweden January 13, 1941 Among the substances which, especially lately, have come into use as preservatives forwood and other organic materials are salts of arsenic acid and hydrofluoric acid. Such salts are very efiective against WOOd destroyers. In applying them, efforts have been made to precipitate these salts in the material in a diflicultly soluble form in order to prevent their leaching out. Certain methods have given successful results with arsenic acid, while hydrofluoric acid has not [been sufliciently fixed, but has been leached out of the wood.

The object of the present invention is the provision of wood preservatives, containing both arsenic acid and hydrofluoric acid and in which both the arsenic and the hydrofluoric acids are precipitated in the material in a diflicultly soluble form.

The preservatives according to the present invention consist of acid solutions or pastes containing (a) arsenic acid and/or alkali metal arsenate, (b) hydrofluoric acid and/or alkali metal fluoride, and (c) bichromate and/or chromate and/or chromic acid and, in addition, either (1) salts of one or more metals which are capable of forming both difiicultly soluble arsenates and difficultly soluble fluorides, or (2) salts of two or more metals of which one or more are capable of forming only diflicultly soluble arsenates and the other or others are capable of forming only dilficultly soluble fluorides. For this purpose, soluble salts of the metals Ca, Mg, Zn or A1 are preferred.

When such a preservative has been introduced into the wood it is supposed that the following reactions take place. Certain substances in the wood will reduce the hexavalent chromium of the chromium compound to a tervalent form, causing precipitation of diificultly soluble chromium arsenates. These reactions reduce the acidity ofthe preservative; other arsenates and fluorides difiicultly soluble in water which are present or produced in the preservative will consequently also be precipitated.

When elaborating the present preservatives it was found that zinc and aluminium salts are the most suitable metal salts for fixing the arsenic acid, and that the presence of both these metal salts in the preservatives will facilitate the dissolution of the salt mixture and improve the durability of the solution. For fixing the hydrofluoric acid calcium and magnesium salts were found most suitable.

The following schedule gives the limits for the 9Claims. (Cl.16738.5)

2 composition of suitable preservatives accordingto the present invention.

Parts N azCrzOmZHzO 6-15 Ala (S04) 3.181-120 0 25 znso nnzo 0-25 NazHAsOn'lI-IzO 0-20 H3AsO4./ H2O 5-20 NaF '1-10 Ca(NO3)2.4H2O 0r Mg-SO4.7H2O 5-30 The proportions must not be varied arbitrarily within the above limits: The preservatives must contain 1-20 parts of arsenic pentoxide (AS205) to 1 part of fluorine (F) and 2-5 parts of arsenic pentoxide to 1 part of chromium (Cr). The preservative must moreover contain sufiicient chromium compounds and metal salts for the effective fixation of both the arsenic and the fluorine in form of diflicultly soluble compounds and the acidity of the preservative must be suflicient to keep the salts dissolved in water. In practice, impregnating solutions are used in which the arsenic pentoxide and fluorine contents are about 1 per cent by weight of the solution.

The following is given as an example of a preservative composed according to the present invention.

Per cent Na2Cr20'L2H2O 14 A12 (S04) 3.18H2O 16 Na2HAsO4.7H2O 15 HsAsO4.%H2O 18 NaF 7 Ca(NO3)2.4HzO or MgSO4.7H2O 2 3 Having thus described my invention I declare that what I claim is:

l. A wood preservative composition characterized in that it contains (a) an arsenic compound selected from the class consisting of arsenic acid and alkali metal arsenates, (b) a fluorine compound selected from the class consisting of hydrofluoric acid and alkali metal fluorides, (c) a chromium compound selected from the class consisting of chromic acid, alkali metal bichromates and alkali metal chromates, and (d) at least one water-soluble salt of at least one of the metals selected from the class consisting of Ca, Mg, Zn

and Al; said composition being further characterized in that, upon treatment of wood, both diflicultly soluble arsenates and difiicultly soluble fluorides are formed in the wood in situ.

and A1; said composition being further characterized. in that, upon treatment of wood, both diflicultly soluble arsenates and difficultly soluble fluorides are formed in the wood in situ.

3. A wood preservative characterized by the following composition:

i Parts N a2Cr2O'1.2I-I2O 6-15 A12(SO4) 3.18H2O -25 ZHSO4.7H2O -.4 0-25 NarHAsOa'IHzO 020 H3ASO4. H2O -20 NBF -.i 1-10 CB,(NO3)2.4H2O 5-30 4. A wood preservative characterized by having substantially the following composition:

Per cent NaaCnOmZHzO 14 A1z(SO4) 3.181120 16 ZnSO4.'7I-I2O '7 N a2HASO4.7I-I2O H3ASO4. H2O 18 NaF I Ca (N03) 2.4H2O 23 5. A wood preservative according to claim 1 characterized by containing 1-20 parts of arsenic pentoxide (AS205) to 1 part of fluorine (F).

6. A wood preservative according to claim 1, characterized by containing 2-5 parts of arsenic pentoxide (AS205) to 1 part of chromium (Cr).

I. A wood preservativecharacterized by the following composition:

- Parts Na2Cl20'z.2H2O 6-15 A12(SO4)3.18H2O 0-25 ZnSO4.7H2O 0-25 NazHASO4.7H2O 0-20 I-I:iAsO4. :HzO 5-20 NaF 1-10 MgSO4.7H2O 5-30 ,8. A wood preservative characterized by having substantially the following composition:

' Per cent Na2Ci2O7.2H2O 14 A1a(SO4) 3.181120 16 ZnSO-rflI-IzO '7 Na2HAsO4.7H2O 15 H3ASO4. H2O 18 NaF 7 MgSO4.7H2O 23 9. A wood preservative according to claim 2, characterized by an ASaOs/F ratio of 1 to 20 parts of the former to 1 part of the latter, and by an ASzOs/Cr ratio of 2 to 5 parts of the former to 1 part of the latter.

BROR OLOF HAGER. 

